Magnetic fluid poly(ethylene glycol) with moderate anticancer activity

Poly(ethylene glycol) (PEG)-containing magnetic fluids - magnetite (Fe₃O₄) stabilized by sodium oleate - were prepared. Magnetic measurements confirmed superparamagnetic behaviour at room temperature. The structure of that kind of magnetic fluid was characterized using different techniques, including electron microscopy, photon cross correlation spectroscopy and small-angle neutron scattering, while the adsorption of PEG on magnetic particles was analyzed by differential scanning calorimetry and Fourier transform infrared spectroscopy. From the in vitro toxicity tests it was found that a magnetic fluid containing PEG (MFPEG) partially inhibited the growth of cancerous B16 cells at the highest tested dose (2.1 mg/ml of Fe₃O₄ in MFPEG).     

Observation and theoretical description of periodic geometric rearrangement in electronically excited nonstoichiometric sodium-fluoride clusters

We present two-color fs pump-probe spectra of Na2F which were recorded by employing excitation wavelengths around 1208 nm (pump) and ionization wavelengths around 405 nm (probe). The observed oscillatory structure of the signal with a period of 185 fs shows an excellent agreement with our simulated spectra. The employed ab initio Wigner distribution approach provides clear evidence that this observation is caused by photoinduced metal bond breaking followed by a butterfly-type periodic geometric rearrangement.     

The structures of vanadium oxide cluster-ethene complexes. A combined IR multiple photon dissociation spectroscopy and DFT calculation study

Infrared spectra of complexes of small vanadium oxide clusters with ethene are determined using infrared multiple photon dissociation (IR-MPD) spectroscopy in the range of 550-1850 cm-1. The structures of the complexes have been identified by comparison of the experimental spectra with the harmonic vibrational frequencies and corresponding IR intensities of possible isomers calculated with DFT methods. We find that the ethene molecule binds directly to a vanadium atom in the cluster, although this it is not in all cases the most stable arrangement.     

Non-adiabatic dynamics of pyrrole: Dependence of deactivation mechanisms on the excitation energy

Non-adiabatic dynamics simulations were performed for pyrrole at time-dependent density functional theory level using the trajectory surface hopping approach. Initial conditions were prepared based on the UV-absorption spectrum so as to simulate monochromatic absorption in three distinct spectral regions. The results showed predominance of the NH-stretch mechanism for excited-state relaxation. With increasing initial energy, however, other mechanisms are activated as well, even though they still occurred for a minor fraction of the trajectories. Dynamics starting at the origin of the absorption spectrum exhibited internal conversion to the ground state with a time constant of 20 fs. In contrast, dynamics starting at higher energies gave rise to much longer time constants for internal conversion near 200 fs.     

Photoinduced superoxide radical anion and singlet oxygen generation in the presence of novel selenadiazoloquinolones (an EPR Study)

Novel 7‐substituted 6‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐h]quinoline ( SeQ(1–6) ) and 8‐substituted 9‐oxo‐6,9‐dihydro[1,2,5]selenadiazolo[3,4‐f ]quinoline derivatives ( SeQN(1–5) ) with R₇, R₈ = H, COOC₂H₅, COOCH₃, COOH, COCH₃ or CN were synthesized and their spectral characteristics were obtained by UV/Vis spectroscopy. Ultraviolet A photoexcitation of the selenadiazoloquinolones in dimethylsulfoxide or acetonitrile resulted in the formation of paramagnetic species coupled with molecular oxygen activation generating the superoxide radical anion or singlet oxygen, evidenced by electron paramagnetic resonance spectroscopy. The cytotoxic/photocytotoxic impact of selenadiazoloquinolones on murine and human cancer cell lines was demonstrated using the derivative SeQ5 (with R₇ = COCH₃).     

Vibrational analysis of 1-methyl-pyridinium-2-aldoxime and 1-methyl-pyridinium-4-aldoxime cations

Pyrimidinium aldoximes are administered intravenously in cases of acute organophosphate poisoning. Since questions regarding their morphology and active conformation in the solution are still open, an effort was made to establish correspondence between their crystal state conformers and vibrational spectra, thus facilitating the future work on the assignment of bands in solution. Normal coordinate analysis including the potential energy distribution for all modes was performed for 1-methyl-pyridinium-2-aldoxime (PAM2AN) and 1-methyl-pyridinium-4-aldoxime (PAM4AN) cations (charge=+e, spin=0). Positions of infrared and Raman bands of corresponding chloride salts agree rather well with predicted values, except for modes taking part in hydrogen bonding to anions. The strength of hydrogen bonding is estimated to be of medium strength in both salts, the bonding in PAM2AN being stronger. The calculated and observed values of the characteristic stretching modes for the aldoxime moiety have been in accordance with the stronger acidity of PAM2AN structural isomer.     

The structural instabilities in ferronematic based on liquid crystal with negative diamagnetic susceptibility anisotropy

The studied ferronematic is a nematic liquid crystal (ZLI1695) of low negative anisotropy of the diamagnetic susceptibility (χ_a<0) doped with the magnetic particles Fe₃O₄. Structural instabilities are interpreted within Burylov and Raikher's theory. The high magnetic fields were oriented perpendicular (Freedericksz transition) or parallel to the initial director. Using capacitance measurements the Freedericksz threshold magnetic field of the ferronematic B_FN, and the critical magnetic field B_max, at which the initial parallel orientation between the director and the magnetic moment of magnetic particles breaks down, have been determined. The values of these quantities have been used to estimate the surface density of the anchoring energy W of liquid crystal molecules on the surface of the magnetic particles. The obtained values indicate a soft anchoring of the liquid crystal on the magnetic particles with a preferred parallel orientation of the magnetic moment of magnetic particles and the director.     

Kinetic analysis of the reaction between (V2O5)n=1,2+ and ethylene

A systematic experimental and theoretical investigation of the influence of reactant energy on the reactivity of (V(2)O(5))(n)=1,2(+) clusters with ethylene (Justes, D. R.; Mitri?, R.; Moore, N. A.; Bonaci?-Koutecky, V.; Castleman, A. W., Jr. J. Am. Chem. Soc., 2003, 125, 6289) provided evidence of the rate controlling steps in the reaction. Herein, we present further experimental and theoretical evidence for our recently proposed radical cation mechanism for oxygen atom transfer from (V(2)O(5))(n)=1,2(+) clusters to ethylene. In particular the results of ab initio molecular dynamics simulations are found to further support the radical cation mechanism. Experimental reaction cross sections at the zero pressure limit and rate coefficients show that the energy dependence of the reaction cross section is in accord with the Langevin formula. Evidence is presented that ion-molecule association is the rate determining step, whereas subsequent hydrogen transfer and formation of acetaldehyde proceed without significant barriers. We propose a kinetic model for the reaction cross section that fully accounts for the experimental findings. The model offers the prospect of elucidating the details of the general reaction mechanisms through a study of the energy dependence of the reaction cross sections.     

Photoabsorption and photofragmentation of isolated cationic silver cluster-tryptophan hybrid systems

We present a theoretical study of the size and structure selective absorption properties of cationic silver cluster-tryptophan Trp-Ag(n)(+) (n = 2-5,9) hybrid systems supported by photofragmentation experiments. Our time-dependent density functional theory calculations provide insight into the nature of excitations in interacting nanoparticle-biomolecule subunits and allow to determine characteristic spectral features as fingerprints of two different classes of structures: charge solvated and zwitterionic. Moreover, different types of charge transfer transitions have been identified. Charge transfer from pi system of tryptophan to silver cluster occurs for charge solvated structures while charge transfer from silver to the NH(3) (+) group takes place for zwitterionic structures. This has been confirmed by experimentally measured photofragmentation channels and molecular dynamics simulations. Our findings provide fundamental insight into the structure- and size-dependent mechanism responsible for the enhanced absorption and emission in nanoparticle-biomolecular hybrid systems.